Molecular Modeling of Stereo- and Regioselectivity of Group 4 Heterocenes in the Polymerization of Propene

Abstract

We report a theoretical analysis on the stereo- and regiochemical behavior of the S- and N-based group 4 heterocenesdeveloped by Ewen, Elder, and Jonesin the polymerization of propene to isotactic polypropylene. Somewhat surprisingly, the polymers produced with the N-based heterocene were shown to present a sensibly smaller amount of regiomistakes and a higher amount of stereomistakes relative to the S-based heterocene. To clarify the different mechanistic behavior of these structurally rather similar catalysts, we compared their stereo- and regioselectivity, and we extended our modeling to the corresponding all-carbon bis(indenyl)-based catalyst. Our analysis supports most of the ideas proposed by Ewen, Elder, and Jones to rationalize the experimental behavior.

Stereoselective and regioselective propylene polymerization with group 4 bisphenolate ether complexes

“…The configuration of the stereogenic center at carbon (H, h, Fig. 1) indicates that the enantioface selectivity of an occasional 2,1‐insertion of propylene into a growing polymer chain is opposite that of the primary 1,2‐insertion, as observed previously for isospecific C 2 ‐symmetric metallocene catalysts1, 44, 46, 47 and octahedral C 2 ‐symmetric bis(phenoxyamine) group 4 catalysts 48. The presence of both 2,1‐erythro RE 1 and 2,1‐threo RE 2 regioerrors indicates that following a 2,1‐insertion, the enantioselectivity for the next primary 1,2‐insertion can vary depending on the nature of the metal and the ligand.…”

“…50 For C 2 -symmetric metallocene catalysts, more highly isospecific catalysts manifest a preference for 2,1-erthyro regioerrors, whereas less stereospecific catalysts generate a mixture of 2,1-erthro and 2,1-threo, where the 2,1-erthyro errors predominate. 1,44,46,47 Isospecific C 2 -symmetric amine(bisphenolate) catalysts 13,31 exhibit a preference for 2,1-erthyro regioerrors, 48 and a carbazole-substituted analog of 4 (R ¼ carbazole) also produces both 2,1-erythro and 2,1-threo regioerrors, albeit in much lower amounts than that for 6a,b. 8 The nature of the ligands also influences the regioselectivity: for the more stereoselective t-butyl-substituted complexes 4a,b and carbazole-substituted complexes 6a,b, the regioselectivity is higher and only the 2,1-erythro regioerrors (RE 1 ) are observed [ Fig.…”

“…A high selectivity for the 2,1‐threo regioerror was observed previously for the monocyclopentadienyl amidinate catalysts;49 in this case, the enantioface preferences was rationalized on the basis of insertion into different enantiotopic coordination sites of the C s ‐symmetric complexes 50. For C 2 ‐symmetric metallocene catalysts, more highly isospecific catalysts manifest a preference for 2,1‐erthyro regioerrors, whereas less stereospecific catalysts generate a mixture of 2,1‐erthro and 2,1‐threo, where the 2,1‐erthyro errors predominate 1, 44, 46, 47. Isospecific C 2 ‐symmetric amine(bisphenolate) catalysts13, 31 exhibit a preference for 2,1‐erthyro regioerrors,48 and a carbazole‐substituted analog of 4 (R = carbazole) also produces both 2,1‐erythro and 2,1‐threo regioerrors, albeit in much lower amounts than that for 6a , b 8…”

Extent of structural change during the reaction and its relationship to isoselectivity in polypropylene polymerization with ansa‐zirconocene/borate catalyst: A computational study

“…Experiments were compared with DFT calculations to examine the olefin monomer selectivity of a metallocene catalyst . Several heterocenes, in which heteroatoms are contained in ligands, were studied with respect to their influence on regio‐/stereoselectivity . The regioselectivity of propylene was examined for various group four metallocene species .…”

“…[26,27] Several heterocenes, in which heteroatoms are contained in ligands, were studied with respect to their influence on regio-/ stereoselectivity. [28] The regioselectivity of propylene was examined for various group four metallocene species. [29] More recently, in the 2010s, a correlation between ligand substitution and regio-/stereocontrol in iPP polymerization with C 2 -symmetric ansa-zirconocene was indicated by both DFT calculations and experiments.…”